Generally speaking, the portion and components of a human eye with which the present invention is most closely concerned, though well known to those skilled in the art, are illustrated and labeled for lexicographic purposes in FIG. 1 of the hereto appended drawings. The eyeball (which is suspended in the orbit by various types of tissues and muscles and is protected in front by the upper and lower eyelids, all not shown) is enclosed in three layers or coats of which only the outer one, the sclera, is explicitly represented (the other layers being the retina and the choroid coat). At the front of the eye, the place of the sclera, which is white and opaque, is taken by the cornea, which is transparent and adjoins the sclera at the limbus under the conjunctiva. The posterior part of the eyeball is enclosed by Tenon's capsule which is connective tissue that extends anteriorly to the conjunctival fornix and is continuous with the muscular fascia of the eye. Interiorly of the eyeball and located behind the cornea are the iris and the lens, with the lens being suspended in place by the ciliary zonule or zonular fibers which are connected at one end to the lens and at the other end to the ciliary body. The iris, which normally rests against the front of the lens (although for the sake of clarity it is shown in FIG. 1 as being spaced somewhat therefrom) is actually a continuation of the choroid coat starting from a location just anteriorly of the ciliary body and is provided in the middle with a circular opening, the pupil, through which light entering the eye through the cornea is able to reach the lens. The space between the cornea and the iris constitutes the anterior chamber of the eye, with the peripheral channel or groove where the cornea and the iris meet in the limbal region of the eye constituting the angle of the anterior chamber. The space between the iris and the lens constitutes the posterior chamber. These two chambers, which communicate through the pupil, are filled with a watery fluid, the aqueous humor. The space in the eyeball behind the lens is filled with a transparent jelly-like substance, the vitreous humor. The lens itself includes a viscous nucleus of inert material enclosed by layers of fibers which in turn are surrounded by an elastic membrane or capsular bag. That part of the capsular bag which is located at the side of the lens facing toward the iris and the cornea is designated the anterior capsule, and that part of the capsular bag which is located at the side of the lens facing toward the retina and engaging the hyaloid face of the vitreous humor is designated the posterior capsule. The hyaloid face is a skin-like somewhat denser region of the vitreous humor which constitutes the boundary of the latter at its interface with the posterior capsule and the ciliary zonule. The cornea, the aqueous humor, the lens and the vitreous humor constitute the refractive media through which light entering the eye passes prior to reaching the retina, with the cornea constituting the main light-refracting structure while the lens, a relatively minor part of the overall optical system, constitutes principally the means of varying the focus.
As is well known, human beings, especially elderly persons, tend to develop a degree of opacity or clouding of the lens fibers surrounding the inert nucleus. The condition where this opacity spreads into the center of the lens in the region behind the pupil so as to impair vision, is designated cataract. When the opacity has progressed sufficiently to cause the loss of useful functional vision, the cataract is said to be mature, and the only currently available treatment for that condition is the removal of the cataract by extraction of the lens from the eye. Such a cataract removal, which is a very delicate operation but probably one of the most common and widely performed ophthalmic surgical procedures these days, may involve either an intracapsular or an extracapsular extraction of the lens.
In an intracapsular cataract extraction (ICCE), the entire lens, including the nucleus, the cortex (the fibers) and the enveloping capsular bag, is taken out as a unit, with the zonular fibers which connect the bag to the ciliary body being first dissolved and the cataract then being removed with the aid of a low temperature probe. In such a case, it was initially the practice, in the early stages of the development of artificial lenses, to follow up the removal procedure by the implantation of an intraocular lens (IOL) into the anterior chamber of the eye, with the lateral position fixation elements or haptics (resilient loops, arms, or the like) of the IOL being received in the angle of the anterior chamber. However, as the structural and functional characteristics of intraocular lenses were modified and improved over the years and as the surgical techniques and skills for the successful implantation of such lenses have become more refined and sophisticated, it became acceptable, as a follow-up to an ICCE, to implant the IOL in the posterior chamber, with the haptics or position fixation elements being received in the ciliary sulcus (which is the juncture region between the iris and the ciliary body and is generally shallow or flat but, merely for the sake of clarity, has been illustrated in FIG. 1 in a somewhat exaggerated fashion as having the form of a relatively deep channel or groove), subject to the provision that steps are taken to ensure that the IOL does not fall into the vitreous humor.
In an extracapsular cataract extraction (ECCE), by way of contrast, first a major portion of the anterior capsule is cut away, leaving in place only that part of the natural or endogenous capsular bag which consists of the posterior capsule and the remaining, generally annular, anterior capsular flap. Then the lens nucleus is extracted from the capsular bag by any well-known type of expression or by phacoemulsification, and finally the cortex is removed by irrigation and aspiration. In such a case, the current practice is to follow up the removal procedure by the implantation of an IOL into the posterior chamber of the eye, with the haptics or position fixation elements being received either in the ciliary sulcus, where the residual portion of the endogenous capsular bag constitutes the means for preventing the IOL from falling into the vitreous humor, or in the residual capsular bag itself at the equatorial region thereof, i.e., where the anterior capsular flap adjoins the posterior capsule.
Irrespective of whether the procedure performed is an ICCE or an ECCE, sooner or later the surgeon may be faced with the post-operative necessity of having to implant any of a number of optical or mechanical devices into the patient's eye. The desired implant may, as stated above, be an optical device such as an IOL (which may be a multi-focal lens, or a lens specifically designed for monocular vision, toric vision, low vision, etc., or even a single-lens or multiple-lens system designed to provide an appropriate degree of correction for astigmatism or macular degeneration), or a mechanical device such as a semipermeable membrane to keep the vitreous humor or other fluids from migrating from the posterior chamber into the anterior chamber while permitting passage of such substances as nutrients, electrolytes, aqueous humor, etc., or a partly mechanical, partly optical device such as a pseudo iris to replace a natural iris which has been surgically removed because of mechanical damage, attack by a cancer, etc. While surgical procedures for effecting such implantations have become quite well known and common over the years and generally pose no difficulties to an experienced ophthalmic surgeon, some patients have nevertheless developed more or less severe post-implantation trauma or after-effects in the form of loss of visual acuity or physical pain or both, which may be due to any of a number of different causes, such as, for example, posterior capsular opacification (resulting from migration of residual epithelial cells from the equatorial region of the capsular bag onto and over the posterior capsule to the medial region thereof intersecting the optical axis of the patient's eye), decentration of the IOL (resulting from a lateral shifting of the IOL out of its desired optimum position either during or after the implantation thereof), etc.
In U.S. Pat. No. 4,888,016, there are disclosed a number of "spare parts," having a variety of structures and shapes, which are designed for implantation into an eye as an adjunct to cataract surgery, principally to facilitate the repair and/or reinforcement and/or replacement of damaged or diseased eye components. Basically, such "spare parts" are artificial members made of cohesive sheet materials of biocompatible substances such as cross-linked hyaluronic acid (including the sodium, potassium and other salts of the acid), polymethyl methacrylic acid (PMMA), silicone, hydrogel or other equivalent substances. One of the types of "spare parts" disclosed in the said patent is a sheet member which has been preformed into the shape and configuration of an artificial capsular bag-like structure that either is an anteriorly incomplete but posteriorly complete capsular bag, i.e., it is a capsular bag-shaped structure having a full posterior capsule portion and an annular anterior capsular flap-like portion connected along its outer periphery to the outer periphery of the posterior capsule portion (i.e., equatorially of the bag), or is a both anteriorly and posteriorly incomplete capsular bag, i.e., a generally toroidal ring-shaped structure having an annular posterior capsular flap-like portion and an annular anterior capsular flap-like portion and thus being essentially similar in form to the original endogenous capsular bag with the central regions of the anterior and posterior capsules both cut away. That type of "spare part" is described in the '016 patent as being designed for surgical implantation either into the residual endogenous capsular bag which remains in the patient's eye after an extracapsular cataract extraction (in this case the exterior peripheral regions of the anterior and posterior capsule portions of the "spare part" are smooth-surfaced) or into the region of the eye which is surrounded by the ciliary body and from which the entire original endogenous capsular bag has been removed by an intracapsular cataract extraction (in this case the "spare part" is provided along the exterior peripheral surface regions of its anterior and posterior capsule portions with a plurality of circumferentially distributed, generally radially extending artificial zonular fibers, also made of the hyaluronic acid or comparable sheet material, to enable the "spare part" to be connected to and supported by the ciliary body).
In U.S. Pat. No. 5,366,501, there is disclosed a "spare part" in the form of an IOL which is specially designed to help prevent the post-operative occurrence of posterior capsular opacification following an ECCE. To this end, the IOL is provided with a dual 360.degree. haptic structure in the form of a pair of concentric rings encircling the central optic or lens body. Of these haptics, the inner ring is spaced from and secured to the outer periphery of the optic by an opposed pair of diametrically aligned generally rod-shaped first bridging elements, while the outer ring is spaced from and secured to the outer periphery of the inner ring by an opposed pair of diametrically aligned generally rod-shaped second bridging elements which are aligned with the first bridging elements and are so oriented as to dispose the inner haptic posteriorly offset somewhat relative to the outer haptic. By virtue of this construction, when such an IOL is implanted in the residual capsular bag of the eye, the outer haptic (which is seated in the equatorial region of the capsular bag) serves as a primary barrier against migration of epithelial cells from the equatorial region of the bag onto the posterior capsule, and the inner haptic (which bears against the anterior surface of the posterior capsule at a location between the equatorial region and the mid-region of the posterior capsule) serves as a secondary barrier for blocking migration into the mid-region of the posterior capsule of any epithelial cells that were not blocked by the outer haptic. At the same time, the offset between the inner and outer haptics also ensures that the optic is pressed against the posterior capsule so as to inhibit the formation of Elschnig's pearls on the posterior capsule.